Home › Chemistry › Stoichiometry Calculator

Stoichiometry Calculator

Parses a balanced chemical equation, converts the given reactant masses or moles to moles, identifies the limiting reagent from mole-to-coefficient ratios and reports the theoretical yield (moles and grams) of every product and the amount of excess reactant left over.

When to use

You have a balanced equation and the amount of one or two reactants and need the limiting reagent, the maximum product mass or moles, or how much of the other reactant remains.

Do not use when: You only need the molar mass of one substance (use molar-mass), a grams-to-moles conversion (use moles-mass), or the percent yield from a measured product mass (use percent-yield after this calculator).

Formula

n_i = mass_i / M_i; ξ = min over known reactants of n_i / ν_i (the reactant giving the minimum is limiting); moles_product = ν_product × ξ; theoretical_yield_g = ν_product × ξ × M_product; excess_remaining = n_excess − ν_excess × ξ

Atom balance is checked with the same formula parser as molar-mass (charges are not balanced). Reactants without a stated amount are assumed to be in excess. Molar masses use IUPAC 2021 abridged atomic weights.

Inputs

ParameterTypeUnitRequiredDescription
equationstringyesBalanced chemical equation with coefficients and formulas, e.g. 2H2 + O2 -> 2H2O or 3Si + 2N2 = Si3N4 (arrow: ->, =, →; states such as (aq) are ignored; write ion charges as Cu^2+ because Cu2+ is read as two copper atoms). An unbalanced equation is rejected.
given_formulastringyesFormula of the reactant whose amount is known; must appear on the left side of the equation.
given_mass_gnumbergnoMass of the given reactant in grams (alternative to given_moles). Range: > 0
given_molesnumbermolnoAmount of the given reactant in moles; takes precedence over given_mass_g. Range: > 0
second_formulastringnoFormula of a second reactant with a known amount, for limiting-reagent analysis. Omit to treat the given reactant as limiting.
second_mass_gnumbergnoMass of the second reactant in grams (alternative to second_moles). Range: > 0
second_molesnumbermolnoAmount of the second reactant in moles; takes precedence over second_mass_g. Range: > 0

Outputs

OutputTypeUnitDescription
balanced_equationstringThe parsed equation with its coefficients, confirming the atom balance.
limiting_reagentstringReactant with the smallest moles ÷ coefficient ratio among those with a known amount.
limiting_reagent_molesnumbermolAmount of the limiting reagent available.
extent_of_reaction_molnumbermolξ = moles of limiting reagent ÷ its coefficient; every species changes by coefficient × ξ.
main_productstringFirst product in the equation, to which the theoretical-yield outputs refer.
theoretical_yield_gnumbergMaximum mass of the main product.
theoretical_yield_molesnumbermolMaximum moles of the main product.
excess_reagentstringThe other reactant with a known amount (only when second_formula is given).
excess_remaining_molesnumbermolMoles of the excess reagent left after complete reaction.
excess_remaining_gnumbergMass of the excess reagent left after complete reaction.
reactantslistPer reactant: formula, coefficient, molar mass, moles and mass consumed, and (when known) moles/mass available, moles/mass in excess and role.
productslistPer product: formula, coefficient, molar mass, moles and mass formed (theoretical yields).

Example

3Si + 2N2 -> Si3N4 with 2.00 g Si and 1.50 g N2: {"equation":"3Si + 2N2 -> Si3N4","given_formula":"Si","given_mass_g":2,"second_formula":"N2","second_mass_g":1.5} → {"limiting_reagent":"Si","limiting_reagent_moles":0.071212,"extent_of_reaction_mol":0.023737,"main_product":"Si3N4","theoretical_yield_g":3.33,"theoretical_yield_moles":0.023737,"excess_reagent":"N2","excess_remaining_moles":0.00607,"excess_remaining_g":0.17}

2H2 + O2 -> 2H2O with 4.0 g H2 and 16.0 g O2: {"equation":"2H2 + O2 -> 2H2O","given_formula":"H2","given_mass_g":4,"second_formula":"O2","second_mass_g":16} → {"balanced_equation":"2 H2 + O2 → 2 H2O","limiting_reagent":"O2","theoretical_yield_g":18.016,"theoretical_yield_moles":1.00006,"excess_reagent":"H2","excess_remaining_g":1.9839,"excess_remaining_moles":0.98406}

GET https://tttkmbb.com/api/v1/calculate/stoichiometry?equation=3Si+%2B+2N2+-%3E+Si3N4&given_formula=Si&given_mass_g=2&second_formula=N2&second_mass_g=1.5

Machine access

Sources

FAQ

What if I only know the amount of one reactant?

Omit second_formula: the given reactant is treated as limiting and the yields assume every other reactant is present in excess.

Why is my equation rejected as unbalanced?

Atom counts of every element must match on both sides, e.g. H2 + O2 -> H2O fails because oxygen is 2 on the left and 1 on the right. The error lists each element that differs; charges of ions are not checked.

Which product does theoretical_yield_g refer to?

The first product written in the equation (main_product); the products list gives the yield of every product.

Related calculators